Working vehicle and working vehicle control method

ABSTRACT

A working vehicle is provided with a hydraulic pump is driven using an engine. A hydraulic actuator is driven using hydraulic fluid which is discharged from the hydraulic pump. A power generator motor driven using the engine. An electric actuator is driven using electrical power which is generated using the power generator motor. An exhaust processing apparatus cleans exhaust from the engine. A reducing agent tank retains reducing agent which is supplied to the exhaust processing apparatus. A retention amount detecting section detects the retention amount of the reducing agent inside the reducing agent tank. An engine control section performs output restriction control where the output of the engine is reduced when the retention amount is equal to or less than a first threshold. The electric actuator control section restricts the output of the electric actuator during executing of the output restriction control.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2015/074848, filed on Sep. 1, 2015.

BACKGROUND

The present invention relates to a working vehicle and a working vehicle control method.

FIELD OF THE INVENTION

A working vehicle is provided with an engine, a hydraulic pump which is driven using an engine, and a hydraulic actuator which is driven using hydraulic fluid which is discharged from the hydraulic pump. The hydraulic actuator is, for example, a hydraulic cylinder and drives a work implement which has a boom, an arm, and the like. In this type of working vehicle, the hydraulic pump is controlled so that the absorption torque of the hydraulic pump does not exceed the output torque of the engine.

At the same time, the working vehicle is provided with an exhaust processing apparatus which cleans exhaust from the engine using reducing agent. In this type of working vehicle, the reducing agent is retained in a reducing agent tank, but there is a possibility that processing of exhaust is not appropriately performed when the retention amount of the reducing agent inside of the reducing agent tank is reduced to low levels. For this reason, control is performed so that the output of the engine is reduced and absorption torque of the hydraulic pump is reduced when the retention amount of the reducing agent is reduced to be lower than a predetermined amount in, for example, a working vehicle in Japanese Unexamined Patent Application Publication No. 2015-71973. Due to this, it is possible to prompt an operator to replenish the reducing agent.

SUMMARY

A hybrid working vehicle, which is provided with a power generator motor which is driven using the engine and an electric actuator which is driven using electrical power which is generated using the power generator motor along with the hydraulic pump and the hydraulic actuator, is being developed in recent years. For example, a hybrid hydraulic excavator is provided with a hydraulic cylinder for driving a work implement and an electric motor for revolving a revolving body.

In this type of hybrid working vehicle, it is desirable to as efficiently as possible secure operation of both hydraulic equipment and electrical equipment in a case where control is performed so that the output of the engine is reduced when the retention amount of the reducing agent is reduced to low levels. However, even when it is possible for operation of the electrical equipment to be easily secured only by reducing the absorption torque of the hydraulic pump as in the prior art, it is difficult for operation of the hydraulic equipment to be secured with the output of the engine mainly used for the electrical equipment.

An aspect of the present invention is to as efficiently as possible secure operation of both hydraulic equipment and electrical equipment in a hybrid working vehicle while reducing the output of an engine when the retention amount of reducing agent is reduced to low levels.

A working vehicle according to one aspect of the present invention is provided with an engine, a hydraulic pump, a hydraulic actuator, a power generator motor, an electric actuator, an exhaust processing apparatus, a reducing agent tank, a retention amount detecting section, an engine control section, and an actuator control section. The hydraulic pump is driven using the engine. The hydraulic actuator is driven using hydraulic fluid which is discharged from the hydraulic pump. The power generator motor is driven using the engine. The electric actuator is driven using electrical power which is generated using the power generator motor. The exhaust processing apparatus cleans exhaust from the engine. The reducing agent tank retains reducing agent which is supplied to the exhaust processing apparatus. The retention amount detecting section detects the retention amount of the reducing agent inside the reducing agent tank. The engine control section performs output restriction control where the output of the engine is reduced when the retention amount is equal to or less than a first threshold. The electric actuator control section restricts the output of the electric actuator during executing of the output restriction control.

In the working vehicle according to this aspect, the output of the engine is reduced and the output of the electric actuator is restricted when the retention amount is equal to or less than the first threshold. For this reason, it is possible for the output of the engine which is distributed to the hydraulic pump to be secured to be large compared to a case where the output of the electric actuator is not restricted. Due to this, it is possible to efficiently secure operation of both hydraulic equipment and electrical equipment in a hybrid working vehicle when the retention amount of the reducing agent is reduced to low levels.

It is desirable that the working vehicle be further provided with an output calculating section, an absorption torque determining section, and a pump control section. It is desirable that the output calculating section calculates the output of the power generator motor which is necessary for driving the electric actuator when the retention amount is equal to or less than the first threshold. It is desirable that the absorption torque determining section determines the absorption torque of the hydraulic pump based on the output of the engine which is reduced and the output of the power generator motor which is necessary for driving the electric actuator. It is desirable that the pump control section controls the hydraulic pump using the absorption torque which is determined.

In this case, the absorption torque of the hydraulic pump is determined based on the output of the engine which is reduced and the output of the power generator motor which is necessary for driving the electric actuator when the retention amount is equal to or less than the first threshold. Here, the output torque of the hydraulic pump which is necessary for driving the hydraulic actuator varies significantly according to the load which is applied to the work implement. Accordingly, it is not easy for the torque which is to be distributed to the hydraulic pump to be accurately estimated during the output restriction control.

In contrast to this, it is possible to accurately estimate the output of the power generator motor which is necessary for driving the electric actuator compared to the output torque of the hydraulic pump which is necessary for driving the hydraulic actuator. Accordingly, it is possible to efficiently determine the output of the power generator motor which is necessary for driving the electric actuator and the absorption torque of the hydraulic pump by first calculating the output of the power generator motor which is necessary for driving the electric actuator and determining the absorption torque of the hydraulic pump based on the result of this calculation. Due to this, it is possible to as efficiently as possible secure operation of both the hydraulic equipment and the electrical equipment in the hybrid working vehicle when the retention amount of the reducing agent is reduced to low levels.

It is desirable that the electric actuator control section stops the electric actuator when the retention amount is equal to or less than a second threshold which is smaller than the first threshold. In this case, it is possible to prompt an operator to replenish the reducing agent.

It is desirable that the working vehicle be further provided with an electrical power control apparatus which is electrically connected with the power generator motor and the electric actuator. It is desirable that the electric actuator control section stops the electrical power control apparatus when the retention amount is equal to or less than the second threshold and predetermined system stop condition is satisfied. In this case, it is possible to prompt an operator to replenish the reducing agent.

It is desirable that the system stop conditions include the operation speed of the electric actuator being reduced to a predetermined speed. In this case, it is possible for the electrical power control apparatus to be stopped in a state where the electric actuator stops or is close to stopping. Due to this, it is possible to avoid the electrical power control apparatus stopping during operation of the electric actuator.

It is desirable that the system stop conditions further include a torque command value to the power generator motor being zero. In this case, it is possible to avoid the electrical power control apparatus from stopping during power generation using the power generator motor. Due to this, it is possible to prevent damage to the electrical power control apparatus due to electrical power which is generated by the power generator motor after stopping of the electrical power control apparatus.

It is desirable that the electric actuator control section sets the torque command value for the electric actuator to zero when the retention amount is equal to or less than the second threshold. Due to this, it is possible to stop the electric actuator.

It is desirable that the engine control section controls the output of the engine with a first engine torque curve during normal periods when the retention amount is larger than the first threshold. It is desirable that the engine control section controls the output of the engine during the output restriction control with a second engine torque curve which stipulates that the output of the engine is lower than in the first engine torque curve. In this case, it is possible to reduce the output of the engine during the output restriction control by changing between engine torque curves.

It is desirable that the electric actuator control section reduces an upper limit for the output torque of the electric actuator during the output restriction control. Due to this, it is possible to reduce the output of the electric actuator during the output restriction control.

It is desirable that the working vehicle be further provided with a traveling body and a revolving body which is supported so that revolving is possible with regard to the traveling body. It is desirable that the electric actuator be an electric motor which revolves the revolving body. In this case, a variation in the load which is applied to the electric motor is small compared to the load which is applied to the hydraulic actuator. For this reason, it is possible to accurately calculate the output of the power generator motor which is necessary for driving the electric actuator.

A working vehicle control method according to another aspect of the present invention is provided with the following steps. A first step is determining a retention amount of reducing agent inside a reducing agent tank. A second step is performing output restriction control where a signal which reduces the output of an engine is output when the retention amount is equal to or less than a first threshold. A third step is outputting a signal for restricting the output of an electric actuator during execution of the output restriction control.

In the working vehicle control method according to this aspect, the output of the engine is reduced and the output of the electric actuator is restricted when the retention amount is equal to or less than the first threshold. For this reason, it is possible for the output of the engine which is distributed to the hydraulic pump to be secured to be large compared to a case where the output of the electric actuator is not limited. Due to this, it is possible to efficiently secure operation of both hydraulic equipment and electrical equipment in a hybrid working vehicle when the retention amount of the reducing agent is reduced to low levels.

It is desirable that the working vehicle control method be further provided with the following steps. A fourth step is calculating the output of a power generator motor which is necessary for driving the electric actuator. A fifth step is determining the absorption torque of a hydraulic pump based on the output of the engine which is reduced and the output of the power generator motor which is necessary for driving the electric actuator. A sixth step is outputting a command signal which indicates the absorption torque of the hydraulic pump which is determined.

In this case, it is possible to efficiently determine the output of the power generator motor which is necessary for driving the electric actuator and the absorption torque of the hydraulic pump by first calculating the output of the power generator motor which is necessary for driving the electric actuator and determining the absorption torque of the hydraulic pump based on the result of this calculation. Due to this, it is possible to as efficiently as possible secure operation of both the hydraulic equipment and the electrical equipment in the hybrid working vehicle when the retention amount of the reducing agent is reduced to low levels.

It is desirable that the working vehicle control method be further provided with the following steps. A seventh step is outputting a stop command to the electric actuator when the retention amount is equal to or less than a second threshold which is smaller than the first threshold. An eighth step is outputting a stop signal for an electric power control apparatus when the operation speed of the electric actuator is reduced to a predetermined speed and a torque command value for the power generator motor is zero after outputting the stop command.

In this case, it is possible to avoid the electrical power control apparatus being stopping during operation of the electric actuator. In addition, it is possible to avoid the electrical power control apparatus being stopped during power generation using the power generator motor. Due to this, it is possible to prevent damage to the electrical power control apparatus due to electrical power which is generated by the power generator motor after stopping of the electrical power control apparatus.

According to exemplary embodiments of the present invention, it is possible to as efficiently as possible secure operation of both the hydraulic equipment and the electrical equipment in the hybrid working vehicle while reducing the output of the engine when the retention amount of the reducing agent is reduced to low levels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective diagram of a working vehicle according to an exemplary embodiment.

FIG. 2 is a schematic diagram illustrating a configuration of an electrical equipment system and a hydraulic equipment system in the working vehicle.

FIG. 3 is a schematic diagram illustrating a configuration of an exhaust processing system in the working vehicle.

FIG. 4 is a schematic diagram illustrating a configuration of a control system in the working vehicle.

FIG. 5 is a diagram illustrating one example of an engine torque curve.

FIG. 6 is a diagram illustrating one example of a pump absorption torque line during multiple operations.

FIG. 7 is a flow chart illustrating processes in output restriction control.

FIG. 8 is a diagram illustrating one example of a derated engine torque curve in output restriction control.

FIG. 9 is a diagram illustrating distribution of engine output torque according to the exemplary embodiment and a comparative example.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A working vehicle according to an exemplary embodiment will be described below with reference to the diagrams. FIG. 1 is a perspective diagram of a working vehicle 100 according to the exemplary embodiment. In the present exemplary embodiment, the working vehicle 100 is a hydraulic excavator. The working vehicle 100 has a vehicle body 1 and a work implement 4.

The vehicle body 1 has a traveling body 2 and a revolving body 3. The traveling body 2 has a pair of traveling apparatuses 2 a and 2 b. Each of the traveling apparatuses 2 a and 2 b have crawler tracks 2 d and 2 e. The working vehicle 100 travels due to the traveling apparatuses 2 a and 2 b driving the crawler tracks 2 d and 2 e.

The revolving body 3 is mounted on the traveling body 2. The revolving body 3 is provided so that revolving is possible with regard to the traveling body 2. The revolving body 3 is revolved due to being driven by a revolving motor 32 (refer to FIG. 2) which will be described later. A driving cab 5 is provided in the revolving body 3. The revolving body 3 has an engine chamber 20. The engine chamber 20 is arranged behind the driving cab 5. The engine chamber 20 accommodates equipment, such as an engine 21 and a hydraulic pump 25 which will be described later.

The work implement 4 is attached to the revolving body 3. The work implement 4 has a boom 7, an arm 8, a working attachment 9, a boom cylinder 10, an arm cylinder 11, and an attachment cylinder 12. A base end portion of the boom 7 is joined to the revolving body 3 so that operation is possible. A front end portion of the boom 7 is joined to a base end portion of the arm 8 so that operation is possible. A front end portion of the arm 8 is joined to the working attachment 9 so that operation is possible.

The boom cylinder 10, the arm cylinder 11, and the attachment cylinder 12 are hydraulic cylinders which are driven using hydraulic fluid which is discharged from the hydraulic pump 25 which will be described later. The boom cylinder 10 operates the boom 7. The arm cylinder 11 operates the arm 8. The attachment cylinder 12 operates the working attachment 9. The work implement 4 is driven by the cylinders 10 to 12 being driven. Here, the working attachment 9 is a bucket in the present exemplary embodiment, but may be another attachment such as a crusher or a breaker.

FIG. 2 is a schematic diagram illustrating a configuration of an electrical equipment system and a hydraulic equipment system in the working vehicle 100. The engine 21 is, for example, a diesel engine. The output horsepower of the engine 21 is controlled by adjusting the amount of fuel which is ejected into the inside of the cylinders of the engine 21. This adjusting is performed by controlling an electronic governor 23, which is installed in a fuel ejection pump 22 of the engine 21, using command signals from a controller 60. A variable speed control type of governor is typically used as the governor 23, and the engine rotation speed and the fuel ejection amount are adjusted according to the load so that the engine rotation speed is the target rotation speed which will be described later. That is, the governor 23 increases and decreases the fuel ejection amount so that there is no longer any difference between the target rotation speed and the actual engine rotation speed.

The actual rotation speed of the engine 21 is detected using an engine rotation speed detecting section 24. The engine rotation speed which is detected using the engine rotation speed detecting section 24 is input to the controller 60 as a detection signal. The output of the engine 21 is distributed between the hydraulic equipment system and the electrical equipment system and this equipment is driven. The hydraulic equipment system will be described below.

The working vehicle 100 has the hydraulic pump 25. The hydraulic pump 25 is joined with the output shaft of the engine 21. The hydraulic pump 25 is driven by the output shaft of the engine 21 being rotated. The hydraulic pump 25 is a variable capacity type of hydraulic pump. The hydraulic pump 25 has a swash plate 26 and the capacity of the hydraulic pump 25 is changed due to changes in the tilting angle of the swash plate 26.

A pump control valve 27 is operated using command signals which are input from the controller 60 and the hydraulic pump 25 is controlled through a servo piston. The pump control valve 27 controls the tilting angle of the swash plate 26 so that the product of the discharge pressure of the hydraulic pump 25 and the capacity of the hydraulic pump 25 does not exceed the pump absorption torque which corresponds to command values (command current values) in the command signals which are input from the controller 60 to the pump control valve 27.

Hydraulic fluid which is discharged from the hydraulic pump 25 is supplied to hydraulic actuators 10 to 14 via an operating valve 28. In detail, hydraulic fluid is supplied to the boom cylinder 10, the arm cylinder 11, the attachment cylinder 12, a right travel motor 13, and a left travel motor 14. The boom 7, the arm 8, and the working attachment 9 are moved by the boom cylinder 10, the arm cylinder 11, and the attachment cylinder 12 being driven. In addition, the traveling apparatuses 2 a and 2 b are moved and the vehicle travels due to the right travel motor 13 and the left travel motor 14 being driven.

The discharge pressure of the hydraulic pump 25 is detected using a discharge pressure detecting section 29. The hydraulic pressure of the hydraulic pump 25 which is detected using the discharge pressure detecting section 29 is input to the controller 60 as a detection signal.

The operating valve 28 is a flow amount and direction control valve which has a plurality of control valves which correspond to each of the hydraulic actuators 10 to 14. The operating valve 28 controls the flow amount of hydraulic fluid which is supplied to each of the hydraulic actuators 10 to 14.

Next, the electrical equipment system will be described. The working vehicle 100 has a power generator motor 31, a revolving motor 32, a power storage apparatus 33, and an electrical power control apparatus 34. The power generator motor 31 is joined with the output shaft of the engine 21. The power generator motor 31 performs a power generating action and an electric moving action depending on the circumstances.

Electrical power is stored in the power storage apparatus 33 due to the power generator motor 31 performing a power generating action. The power storage apparatus 33 is, for example, a capacitor. However, the power storage apparatus 33 is not limited to being a capacitor and may be another type of power storage apparatus. The power storage apparatus 33 supplies electrical power to the revolving motor 32. The power storage apparatus 33 supplies electrical power to the power generator motor 31 when the power generator motor 31 performs an electric moving action.

The power generator motor 31 performs an electric moving action when the output of the engine 21 is insufficient. The power generator motor 31 is driven by electrical power being supplied from the power storage apparatus 33 and the engine 21 is assisted by this.

The revolving motor 32 is an electric motor which is driven by electrical power being supplied from the power storage apparatus 33 or the power generator motor 31. The revolving motor 32 revolves the revolving body 3 described above by being driven using electrical power from the power storage apparatus 33 or the power generator motor 31. In addition, the revolving motor 32 carries out a regenerative operation when the revolving body 3 is decelerating. That is, the revolving motor 32 generates electrical power by regenerating the deceleration energy of the revolving body 3 and supplies the electrical power which is generated to the power storage apparatus 33.

A motor rotation detecting section 35 which detects the rotation speed of the revolving motor 32 is provided in the revolving motor 32. The rotation speed of the revolving motor 32 which is detected using the motor rotation detecting section 35 is input to the controller 60.

The electrical power control apparatus 34 is electrically connected to the power generator motor 31, the revolving motor 32, and the power storage apparatus 33. The electrical power control apparatus 34 controls electrical power which is supplied to the power generator motor 31, the revolving motor 32, and the power storage apparatus 33. The electrical power control apparatus 34 has a first inverter 36, a second inverter 37, and a booster 38.

The first inverter 36 is connected with the power generator motor 31. The second inverter 37 is connected with the first inverter 36 and the revolving motor 32 is connected with the second inverter 37. The booster 38 is connected between the first inverter 36 and the second inverter 37. The booster 38 is connected with the power storage apparatus 33 via a contactor 39.

The contactor 39 is in a conducting state during normal periods due to an electrical circuit between the power storage apparatus 33 and the booster 38 being closed. The contactor 39 puts the state into a cutoff state by opening the electrical circuit according to a command from the controller 60 during periods with abnormalities.

The first inverter 36 converts alternating current electrical power which is generated using the power generator motor 31 to direct current electrical power when electrical power which is generated using the power generator motor 31 is being charged into the power storage apparatus 33. The first inverter 36 converts direct current electrical power which is stored in the power storage apparatus 33 to alternating current electrical power when electrical power is being supplied from the power storage apparatus 33 to the power generator motor 31.

The second inverter 37 converts alternating current electrical power which is generated using the revolving motor 32 to direct current electrical power when electrical power which is generated using the revolving motor 32 is being charged into the power storage apparatus 33. The second inverter 37 converts direct current electrical power which is stored in the power storage apparatus 33 to alternating current electrical power when electrical power is being supplied from the power storage apparatus 33 to the revolving motor 32.

The booster 38 controls the electrical power output from the booster 38 due to being controlled by the controller 60. The booster 38 boosts the voltage of the electrical power which is supplied from the power storage apparatus 33 to the power generator motor 31 via the first inverter 36 when the power generator motor 31 is carrying out an electric moving action. The booster 38 boosts the voltage of the electrical power which is supplied from the power storage apparatus 33 to the revolving motor 32 via the second inverter 37 when the revolving motor 32 is being driven. In addition, the booster 38 lowers the voltage which is supplied to the power storage apparatus 33 when electrical power which is generated using the power generator motor 31 or the revolving motor 32 is being charged into the power storage apparatus 33.

A voltage detecting section 41 is provided between the booster 38 and the first and second inverters 36, 37. The voltage detecting section 41 detects the size of the voltage which is boosted by the booster 38. The voltage which is detected using the voltage detecting section 41 is input to the controller 60.

A current detecting section 42 is provided in the second inverter 37. The current detecting section 42 detects the current which is input into the second inverter 37. The current, which is input to the second inverter 37 and which is detected using the current detecting section 42, is input to the controller 60.

A power storage voltage detecting section 43 is provided in the power storage apparatus 33. The power storage voltage detecting section 43 detects the voltage of the electrical power which is stored in the power storage apparatus 33. The voltage of the electrical power, which is stored in the power storage apparatus 33 and which is detected using the power storage voltage detecting section 43, is input to the controller 60. The controller 60 monitors the amount of charging of the power storage apparatus 33 from the voltage of the electrical power which is stored in the power storage apparatus 33,

The working vehicle 100 has a work implement operating section 15 as shown in FIG. 2. The work implement operating section 15 is operated by an operator to move the work implement 4. The work implement operating section 15 includes, for example, an operating lever. The operating amount of the work implement operating section 15 is input to the controller 60. In detail, the operating amount of the work implement operating section 15 for operating the boom 7 (referred to below as “boom operating amount”), the operating amount of the work implement operating section 15 for operating the arm 8 (referred to below as “arm operating amount”), and the operating amount of the work implement operating section 15 for operating the working attachment 9 (referred to below as “attachment operating amount”) are input to the controller 60.

The operating valve 28 described above is controlled according to the operating amount of the work implement operating section 15. The operating valve 28 modifies the area which is open in the control valves which correspond to each of the hydraulic cylinders 10 to 12 of the work implement 4 according to the operating amount of the work implement operating section 15. As a result, each of the hydraulic cylinders 10 to 12 are moved at speeds according to the operating amount of the work implement operating section 15.

The working vehicle 100 has a travel operating section 16. The travel operating section 16 is operated by an operator to move the right travel motor 13 and the left travel motor 14. The travel operating section 16 includes, for example, an operating lever or an operating pedal. Either of the right travel motor 13 or the left travel motor 14 is driven according to the operating direction of the travel operating section 16. The operating amount of the travel operating section 16 is input to the controller 60. In detail, the operating amount of the travel operating section 16 for operating the right travel motor 13 (referred to below as “right travel operating amount”) and the operating amount of the travel operating section 16 for operating the left travel motor 14 (referred to below as “left travel operating amount”) are input to the controller 60.

The operating valve 28 modifies the area which is open in the control valves which correspond to the right and left travel motors 13 and 14 according to the operating amount of the travel operating section 16. Due to this, the right and left travel motors 13 and 14 are moved at speeds according to the operating amount of the travel operating section 16.

For example, a pilot pressure according to the operating amount of the work implement operating section 15 and the operating amount of the travel operating section 16 may be applied to a pilot port of the operating valve 28. Due to this, the area which is open in each of the control valves in the operating valve 28 are modified according to the respective operating amounts. Alternatively, the operating valve 28 may be electrically controlled using the controller 60. In this case, the controller 60 inputs a command signal according to the operating amount of the work implement operating section 15 and the operating amount of the travel operating section 16 to the operating valve 28.

The working vehicle 100 has a revolving operating section 17. The revolving operating section 17 is operated by an operator to move the revolving motor 32. The revolving operating section 17 includes, for example, an operating lever. The rotation direction of the revolving motor 32 is switched according to the operating direction of the revolving operating section 17. The operating amount of the revolving operating section 17 is input to the controller 60. The controller 60 controls electrical power which is supplied to the revolving motor 32 according to the operating amount of the revolving operating section 17. Due to this, the revolving body 3 revolves at a speed according to the operating amount of the revolving operating section 17.

The working vehicle 100 has a display apparatus 18. The display apparatus 18 displays information on the working vehicle 100, such as the engine rotation speed. The working vehicle 100 has an input apparatus 19. The input apparatus 19 is an apparatus for inputting various types of settings for the working vehicle 100, such as setting the working mode which will be described later. Here, the display apparatus 18 and the input apparatus 19 may be provided to be integrated using a touch panel type of monitor apparatus.

Next, an exhaust processing system of the working vehicle 100 will be described. FIG. 3 is a schematic diagram illustrating a configuration of the exhaust processing system in the working vehicle 100. The working vehicle 100 has a first exhaust processing apparatus 45 and a second exhaust processing apparatus 46 as shown in FIG. 3. The first exhaust processing apparatus 45 is, for example, a diesel particulate filtering apparatus. The first exhaust processing apparatus 45 is connected with the engine 21 and cleans particulate matter (PM) in the exhaust.

The second exhaust processing apparatus 46 is connected with the first exhaust processing apparatus 45 via a mixing pipe 47. The second exhaust processing apparatus 46 is, for example, a selective catalytic reduction apparatus. The second exhaust processing apparatus 46 cleans nitrogen oxides (NOx) in the exhaust with a catalyst using a reducing agent, such as urea water. The exhaust which is cleaned using the first exhaust processing apparatus 45 and the second exhaust processing apparatus 46 is released to the outside of the working vehicle 100 via an exhaust pipe 48 which is shown in FIG. 1.

A reducing agent injector 49 is attached in the mixing pipe 47. The reducing agent injector 49 ejects reducing agent inside the mixing pipe 47. The reducing agent injector 49 is connected with a reducing agent pump 51 and a reducing agent tank 52 via a reducing agent hose 50. The reducing agent tank 52 retains reducing agent. The reducing agent pump 51 draws reducing agent from the reducing agent tank 52 and sends the reducing agent to the reducing agent injector 49.

A retention amount detecting section 53 is provided in the reducing agent tank 52. The retention amount detecting section 53 detects the retention amount of reducing agent inside the reducing agent tank 52. The retention amount detecting section 53 inputs the retention amount of reducing agent which is detected to the controller 60.

Next, controlling which is executed using the controller 60 will be described. FIG. 4 is a schematic diagram illustrating a configuration of the control system in the working vehicle 100. The controller 60 is realized using a computer which has a memory section 62, such as a RAM and a ROM, and a computing section 61, such as a central processing unit (CPU) as shown in FIG. 4. The controller 60 carries out programs to control the engine 21, the hydraulic equipment system, and the electrical equipment system. The controller 60 may be realized using a plurality of computers. The controller 60 has an engine control section 63, a pump control section 64, and an electric actuator control section 65 as shown in FIG. 4.

The engine control section 63 performs control of the engine 21 based on engine torque curves P1 and E1 which are shown in FIG. 5. The engine torque curves P1 and E1 express upper value limits for torque which it is possible for the engine 21 to output according to the rotation speed. That is, the engine torque curves P1 and E1 stipulate the relationship between the engine rotation speed and the upper limit values for the output torque for the engine 21. The engine torque curves P1 and E1 are stored in the memory section 62.

The engine control section 63 determines the target rotation speed for the engine 21 from the operating amount of the work implement operating section 15, the operating amount of the travel operating section 16, and the operating amount of the revolving operating section 17. The operating amount of the work implement operating section 15 is the total of the boom operating amount, the arm operating amount, and the attachment operating amount described above. The operating amount of the travel operating section 16 is the total of the left travel operating amount and the right travel operating amount. The engine control section 63 determines the target rotation speed for the engine 21 according to, for example, the total of the operating amount of the work implement operating section 15, the operating amount of the travel operating section 16, and the operating amount of the revolving operating section 17. The governor 23 controls the output of the engine 21 so that the actual rotation speed of the engine 21 is the target rotation speed while the output torque of the engine 21 does not exceed the engine torque curves.

In FIG. 5, P1 indicates a first engine torque curve. The first engine torque curve P1 is equivalent to the rating of the engine 21 and the maximum power output. The first engine torque curve P1 has a maximum torque point Pt and a rating point Pp. The output torque of the engine 21 is at its maximum at the maximum torque point Pt in the first engine torque curve P1. In addition, the output horsepower of the engine 21 is at its maximum at the rating point Pp in the first engine torque curve Pl.

The output torque of the engine 21 increases according to increases in the engine rotation speed in the first engine torque curve P1 over a range from where the engine rotation speed is a low idle rotation speed NLi to where the engine rotation speed is an engine rotation speed Nt at the maximum torque point Pt. The output torque of the engine 21 falls according to increases in the engine rotation speed over a range from where the engine rotation speed is Nt to where the engine rotation speed is an engine rotation speed Np at the rating point Pp.

A regulation line Rm, where the output torque of the engine 21 suddenly falls due to increases in the engine rotation speed, is stipulated over a range where the rating point Pp is exceeded in the first engine torque curve P1. The regulation line Rm is a line which joins the rating point Pp and a maximum engine rotation speed NHi in a state where there is no load.

The engine control section 63 selects the engine torque curve according to the working mode which is set. The working mode is set due to an operator manipulating the input apparatus 19. There are a P mode and an E mode as the working modes.

The P mode is a working mode where the output torque of the engine 21 is large and which is excellent for workability. The first engine torque curve P1 which is shown in FIG. 5 is selected in the P mode. The E mode is a working mode where the output torque of the engine 21 is smaller than in the P mode and which is excellent for fuel consumption. The second engine torque curve E1 which is shown in FIG. 5 is selected in the E mode. The output torque of the engine 21 is smaller in the second engine torque curve E1 than in the first engine torque curve P1. Here, it may be possible to select a plurality of E modes where the output torque of the engine 21 is reduced in stages.

The pump control section 64 controls the upper limit for the absorption torque of the hydraulic pump 25 based on a pump absorption torque line which is expressed by Lp1 and Le1 in FIG. 5. Lp1 is a pump absorption torque line which corresponds to the first engine torque curve P1. Le1 is a pump absorption torque line which corresponds to the second engine torque curve E1. The pump absorption torque lines Lp1 and Le1 stipulate the relationship with the upper limit for the absorption torque of the hydraulic pump 25 which corresponds to the engine rotation speed. The pump absorption torque lines Lp1 and Le1 are stored in the memory section 62.

The pump control section 64 controls the capacity of the hydraulic pump 25 in the P mode so that the upper limit for the engine output torque and the upper limit for the absorption torque of the hydraulic pump 25 match at a matching point Mp1 with a target rotation speed N1 for the engine 21. In the same manner, the pump control section 64 controls the capacity of the hydraulic pump 25 in the E mode so that the upper limit for the engine output torque and the upper limit for the absorption torque of the hydraulic pump 25 match at a matching point Me1 with the target rotation speed Ni for the engine 21.

Here, the pump absorption torque lines Lp1 and Le1 which are shown in FIG. 5 indicate pump absorption torque lines where the electric actuators such as the revolving motor 32 and the power generator motor 31 are not used and only the hydraulic actuators are used.

The electric actuator control section 65 controls the revolving motor 32 and the power generator motor 31 by controlling the electrical power control apparatus 34. The electric actuator control section 65 controls the revolving motor 32 based on the operating amount of the revolving operating section 17. The electric actuator control section 65 controls the power generator motor 31 based on the actual engine rotation speed, the target rotation speed, the voltage of the power storage apparatus 33, and the like.

For example, when the electric actuator control section 65 ascertains that the output of the engine 21 is insufficient based on the actual engine rotation speed, the target rotation speed, the voltage of the power storage apparatus 33, and the like, the engine 21 is assisted by an electric moving action being carried out by the power generator motor 31. In addition, when the electric actuator control section 65 ascertains that the output of the engine 21 is not insufficient based on the actual engine rotation speed, the target rotation speed, the voltage of the power storage apparatus 33, and the like, the power storage apparatus 33 is charged by a power generating action being carried out by the power generator motor 31.

When the power generator motor 31 is controlled to perform a power generating action, the electric actuator control section 65 determines a torque command value for the power generator motor 31 based on the voltage of the power storage apparatus 33. The electric actuator control section 65 determines a torque command value for the power generator motor 31 so that the voltage for power storage is maintained within a predetermined range. The electric actuator control section 65 controls the power generator motor 31 so that the actual torque of the power generator motor 31 is the torque command value.

The electric actuator control section 65 determines the target revolving speed from the operating amount of the revolving operating section 17. For example, the electric actuator control section 65 increases the target revolving speed according to increases in the operating amount of the revolving operating section 17. The electric actuator control section 65 determines a torque command value for the revolving motor 32 to achieve the target revolving speed from the actual revolving speed. The electric actuator control section 65 controls the revolving motor 32 so that the torque of the revolving motor 32 is the torque command value.

When the power generator motor 31 performs a power generating action, a portion of the engine output torque is used to drive the power generator motor 31. Accordingly, the controller 60 executes energy management where the engine output torque is distributed to the hydraulic equipment system and the electrical equipment system during multiple operations where there is operating of the hydraulic equipment system and the electrical equipment system at the same time. During energy management at normal periods where output restriction control which will be described later is not being executed, the upper limit for the absorption torque of the hydraulic pump 25 is determined in consideration of the engine output torque which is distributed to drive the power generator motor 31.

In detail, the controller 60 has an output calculating section 66 as shown in FIG. 4. The output calculating section 66 calculates the output of the power generator motor 31 which is necessary for driving the revolving motor 32. For example, the output calculating section 66 calculates the electrical power which is needed for driving the revolving motor 32 from the output torque of the revolving motor 32. Then, to obtain the electrical power which is calculated, the output calculating section 66 determines the amount of electrical power which is to be obtained from the power storage apparatus 33 and the amount of electrical power from a power generating action of the power generator motor 31. The ratio of the amount of electrical power which is to be obtained from the power storage apparatus 33 and the amount of electrical power from a power generating action of the power generator motor 31 is determined according to the amount of electrical power which is stored in the power storage apparatus 33. The output calculating section 66 calculates the necessary output horsepower for the engine 21 from the amount of electrical power from a power generating action of the power generator motor 31 and determines an engine output torque Thb (referred to below as “power generator torque Thb”) which is distributed to drive the power generator motor 31 from the necessary output horsepower for the engine 21.

The controller 60 has an absorption torque determining section 67 as shown in FIG. 4. The absorption torque determining section 67 determines the absorption torque of the hydraulic pump 25 based on the power generator torque Thb. In detail, a value Tp2, where the power generator torque Thb is subtracted from an upper limit Tp1 for the pump absorption torque which is determined based on the pump absorption torque line Lp1 described above, is determined as the upper limit for the absorption torque of the hydraulic pump 25 during multiple operations as shown in FIG. 6.

Here, Lp2 in FIG. 6 is a pump absorption torque line for during multiple operations and stipulates the upper limit for the absorption torque which is lower than the pump absorption torque line Lp1 described above by the power generator torque Thb. The pump absorption torque line Lp2 for during multiple operations is modified according to increases and decreases in the power generator torque Thb.

Energy management as described above is executed during multiple operations where there is operating of the electrical equipment system and the hydraulic equipment system at the same time. Due to this, the total of the absorption torque of the hydraulic pump 25 and the power generator torque is controlled to not exceed the engine output torque.

In the working vehicle 100 according to the present exemplary embodiment, the controller 60 executes the output restriction control where the output of the engine 21 is restricted according to the retention amount of the reducing agent inside the reducing agent tank 52. The output restriction control will be described below in detail.

FIG. 7 is a flow chart illustrating processes in the output restriction control. As shown in FIG. 7, in step S1, a retention amount A of the reducing agent inside the reducing agent tank 52 is detected. In step S2, it is ascertained whether the retention amount A is equal to or less than a threshold al. Here, the retention amount A and the threshold al are, for example, proportions of the remaining amount of the reducing agent with the maximum retention amount in the reducing agent tank 52 as 100%. However, the retention amount A and the threshold al are not limited to being proportions of the remaining amount and may be the volume of the reducing agent which remains. The same applies to thresholds a2 to a4 which will be described later.

A first warning is issued in step S3 when the retention amount A is equal to or less than the threshold al. The controller 60 displays the first warning on the display apparatus 18. The first warning is, for example, a display, such as a message, which notifies an operator that the retention amount is low.

Next, in step S4, it is ascertained whether the retention amount A is equal to or less than the threshold a2. The threshold a2 is smaller than the threshold al. A second warning is issued in step S5 when the retention amount A is equal to or less than the threshold a2. The controller 60 displays the second warning on the display apparatus 18. The second warning is, for example, a display such as a message which gives notice that output restriction will be executed when the retention amount is further reduced.

Next, in step S6, it is ascertained whether the retention amount A is equal to or less than the threshold a3. The threshold a3 is smaller than the threshold a2. A first level of output restrictions is executed in step S7 when the retention amount A is equal to or less than the threshold a3.

The engine control section 63 reduces the engine output torque in the first level of output restrictions. In detail, the engine control section 63 outputs a command signal to the governor 23 so that the output of the engine 21 is controlled with a derated engine torque curve D1 as shown in FIG. 8. The derated engine torque curve DI stipulates the upper limit for output torque which is lower than in the engine torque curves P1 and E1 during normal periods when the retention amount A is larger than the threshold a3. In other words, the derated engine torque curve DI stipulates the upper limit for output torque which is lower than in the engine torque curves P1 and E1 which are able to be selected by an operator. The derated engine torque curve DI stipulates the upper limit for output torque which is lower than in the engine torque curves P1 and E1 during normal periods over a range of engine rotation speeds which is at least equal to or more than the maximum torque point Pt.

In addition, the electric actuator control section 65 outputs a command signal to the second inverter 37 in the first level of output restrictions so that the output of the revolving motor 32 is restricted. In detail, the electric actuator control section 65 reduces the upper limit for the torque of the revolving motor 32. For example, the electric actuator control section 65 reduces the upper limit for the torque command value for the revolving motor 32. Due to this, the revolving speed is reduced to be less than the target revolving speed according to the operating amount of the revolving operating section 17.

The absorption torque determining section 67 determines the absorption torque of the hydraulic pump 25 in the first level of output restrictions based on the output of the engine 21 which is reduced due to the first level of output restrictions and the power generator torque Thb. In detail, the engine output torque is reduced in the first level of output restrictions from an upper limit value Te during normal periods to Te′ as shown in FIG. 9. The absorption torque determining section 67 determines the absorption torque Tp′ of the hydraulic pump 25 in the first level of output restrictions by subtracting a power generator torque Thb′ from the engine output torque Te′ which is reduced. The pump control section 64 outputs a command signal, which indicates the absorption torque Tp′ of the hydraulic pump 25 which is determined, to the pump control valve 27. Due to this, the hydraulic pump 25 is controlled using the absorption torque Tp′ which is determined.

Here, the power generator torque Thb′ in the first level of output restrictions is calculated using the output calculating section 66 in the same manner as the power generator torque Thb during normal periods described above. Here, the power generator torque Thb′ in the first level of output restrictions is smaller than the power generator torque Thb during normal periods since the torque command value for the revolving motor 32 is reduced during the first level of output restrictions as described above.

Next, in step S8, it is ascertained whether the retention amount A is equal to or less than the threshold a4. The threshold a4 is smaller than the threshold a3. A second level of output restrictions is executed in step S9 when the retention amount A is equal to or less than the threshold a4.

The engine control section 63 further reduces the engine output torque in the second level of output restrictions compared to the first level of output restrictions. In detail, the engine control section 63 controls the output of the engine 21 with a derated engine torque curve D2 as shown in FIG. 8. The derated engine torque curve D2 stipulates the upper limit for output torque which is lower than in the derated engine torque curve D1. In addition, the derated engine torque curve D2 restricts the upper limit for the engine rotation speed to Nd.

In addition, the electric actuator control section 65 stops the revolving motor 32 in the second level of output restrictions. In detail, the electric actuator control section 65 sets the torque command value for the revolving motor 32 to zero.

Next, in step S10, the electric actuator control section 65 ascertains whether or not predetermined system stop conditions are satisfied. When the predetermined system stop conditions are satisfied, the electric actuator control section 65 outputs a stop command to the electrical power control apparatus 34 in step S11. Due to this, the entire system of the electrical equipment system is stopped.

In detail, the system stop conditions are when both of the following two conditions are satisfied.

-   -   Condition 1—The operation speed of the revolving motor 32 is         reduced to be equal or less than a predetermined speed.     -   Condition 2—The torque command value to the power generator         motor 31 is zero.

Accordingly, the entire system of the electrical equipment system is stopped when the operation speed of the revolving motor 32 is reduced to be equal or less than a predetermined speed and power generating using the power generator motor 31 is stopped after the output torque of the engine is reduced and there is a command to stop the revolving motor 32 due to the second level of output restrictions.

Next, in step S12, it is ascertained whether or not a continuous time period T over which the retention amount A is equal to or less than the threshold a4 is equal to or more than a predetermined time period threshold t1. When the continuous time period T is equal to or more than the predetermined time period threshold t1, a third level of output restrictions is executed in step S13.

The engine control section 63 controls the output of the engine 21 in the third level of output restrictions with a derated engine torque curve D3 as shown in FIG. 8. The engine rotation speed is restricted to the low idle rotation speed NLi in the derated engine torque curve D3.

In the working vehicle 100 according to the present exemplary embodiment which is described above, the first level of output restrictions is performed when the retention amount A of the reducing agent is equal to or less than the threshold a3. The absorption torque Tp′ of the hydraulic pump 25 is determined in the first level of output restrictions based on the engine output torque Te′ which is reduced and the power generator torque Thb′ as shown in FIG. 9. Here, the output torque of the hydraulic pump 25 which is necessary for driving the hydraulic actuators 10 to 14 varies significantly according to the load which is applied to the work implement 4. Accordingly, it is not easy for the torque which is to be distributed to the hydraulic pump 25 to be accurately estimated during the output restriction control.

For example, in a comparative example which is shown in FIG. 9, output torque Thb″ of the power generator motor 31 is determined by subtracting absorption torque Tp″ of the hydraulic pump 25 from the engine output torque Te′ which is reduced. In this case, when the absorption torque of the hydraulic pump 25 is actually Tp′″ which is lower than the estimated value Tp″, the engine output torque which is equivalent to the portion where hatching is applied in FIG. 9 (Tp″-Tp′″) is wasted since it is not absorbed by the hydraulic pump 25 and it is not used in driving the power generator motor 31.

In contrast to this, in the working vehicle 100 according to the present exemplary embodiment, first, the power generator torque Thb′ is calculated and the absorption torque Tp′ of the hydraulic pump 25 is calculated based on the result of this calculation. It is possible to accurately calculate the power generator torque Thb′ from the current value of the revolving motor 32 and the like. For this reason, it is possible to efficiently determine the power generator torque Thb′ and the absorption torque Tp′ of the hydraulic pump 25. Due to this, it is possible to as efficiently as possible secure operation of both the hydraulic equipment and the electrical equipment in the hybrid working vehicle 100 when the retention amount of the reducing agent is reduced to low levels.

The second level of output restrictions is performed when the retention amount A of the reducing agent is equal to or less than the threshold a4. The engine output torque is further reduced and the revolving motor 32 is stopped in the second level of output restrictions. Due to this, it is possible to further prompt an operator to replenish the reducing agent.

In addition, the electric actuator control section 65 stops the electrical power control apparatus 34 when the retention amount A of the reducing agent is equal to or less than the fourth threshold a4 and the system stop conditions are satisfied. Due to this, it is possible to further prompt an operator to replenish the reducing agent since the entire electrical equipment system stops.

The system stop conditions include the operation speed of the revolving motor 32 being reduced to a predetermined speed. For this reason, it is possible for the electrical power control apparatus 34 to be stopped in a state where the revolving motor 32 stops or is close to stopping. Due to this, it is possible to avoid the electrical power control apparatus 34 stopping during operation of the revolving motor 32.

The system stop conditions include the torque command value to the power generator motor 31 being zero. For this reason, it is possible to avoid the electrical power control apparatus 34 from stopping during power generation using the power generator motor 31. Due to this, it is possible to prevent damage to the electrical power control apparatus 34 due to electrical power which is generated by the power generator motor 31 after stopping of the electrical power control apparatus 34.

One exemplary embodiment of the present invention is described above but the present invention is not limited to the exemplary embodiment described above and various modifications are possible within a scope which does not depart from the gist of the invention.

A hydraulic excavator is given as an example of the working vehicle 100 in the exemplary embodiment described above, but the present invention may be applied to other types of working vehicles, such as a wheel loader. The electric actuator is not limited to a revolving motor and may be a motor for travelling, a motor for steering, or an electric actuator other than a motor.

The system stop conditions are not limited to the two conditions described above and may be other conditions. Alternatively, conditions other than the two conditions described above may be added. Alternatively, one of either of the two conditions described above may be omitted.

A portion of the processes in the output restriction control may be omitted or modified. For example, the third level of output restrictions may be omitted.

Restriction of the output of the revolving motor 32 may be executed with the condition that the engine control section 63 executes a process where the engine output torque is reduced. Restriction of the output of the revolving motor 32 may be executed with the condition that the retention amount is equal to or less than a threshold.

According to exemplary embodiments of the present invention, it is possible to as efficiently as possible secure operation of both hydraulic equipment and electrical equipment in a hybrid working vehicle while reducing the output of an engine when the retention amount of reducing agent is reduced to low levels. 

1. A working vehicle comprising: an engine; a hydraulic pump driven by the engine; a hydraulic actuator driven by a hydraulic fluid discharged from the hydraulic pump; a power generator driven by the engine; an electric actuator driven by electrical power generated by the power generator; an exhaust processing apparatus which cleans an exhaust from the engine; a reducing agent tank which retains a reducing agent supplied to the exhaust processing apparatus; a retention amount detecting section which detects a retention amount of the reducing agent inside the reducing agent tank; an engine control section which performs an output restriction control in which an output of the engine is reduced when the retention amount is equal to or less than a first threshold; and an electric actuator control section which restricts an output of the electric actuator during executing of the output restriction control: and an electrical power control apparatus electrically connected with the power generator and the electric actuator, the electric actuator control section stopping the electric actuator when the retention amount is equal to or less than a second threshold which is smaller than the first threshold; and the electric actuator control section stopping the electrical power control apparatus when the retention amount is equal to or less than the second threshold and predetermined system stop conditions are satisfied.
 2. A working vehicle comprising: an engine; a hydraulic pump driven by the engine; a hydraulic actuator driven by a hydraulic fluid discharged from the hydraulic pump: a power generator driven by the engine: an electric actuator driven by electrical power generated by the power generator; an exhaust processing apparatus which cleans an exhaust from the engine; a reducing agent tank which retains a reducing agent supplied to the exhaust processing apparatus; a retention amount detecting section which detects a retention amount of the reducing agent inside the reducing agent tank; an engine control section which performs an output restriction control in which an output of the engine is reduced when the retention amount is equal to or less than a first threshold; an electric actuator control section which restricts an output of the electric actuator during executing of the output restriction control; an output calculating section which calculates the output of the power generator which is necessary for driving the electric actuator when the retention amount is equal to or less than the first threshold; an absorption torque determining section which determines an absorption torque of the hydraulic pump based on the output of the engine which is reduced and the restricted output of the power generator which is necessary for driving the electric actuator which is restricted; and a pump control section which controls the hydraulic pump with the determined absorption torque.
 3. The working vehicle according to claim 2, wherein the electric actuator control section stops the electric actuator when the retention amount is equal to or less than a second threshold which is smaller than the first threshold.
 4. The working vehicle according to claim 3, further comprising an electrical power control apparatus electrically connected with the power generator and the electric actuator, the electric actuator control section stopping the electrical power control apparatus when the retention amount is equal to or less than the second threshold and predetermined system stop conditions are satisfied.
 5. The working vehicle according to claim 4, wherein the predetermined system stop conditions include the operation speed of the electric actuator being reduced to a predetermined speed.
 6. The working vehicle according to claim 5, wherein the predetermined system stop conditions further include a torque command value to the power generator being zero.
 7. The working vehicle according to claim 1, wherein the electric actuator control section sets the torque command value to the electric actuator to zero when the retention amount is equal to or less than the second threshold.
 8. The working vehicle according to claim 1, wherein the engine control section controls the output of the engine with a first engine torque curve during normal periods in which the retention amount is larger than the first threshold, and the engine control section controls the output of the engine during the output restriction control with a second engine torque curve which stipulates that the output of the engine is lower than in the first engine torque curve.
 9. The working vehicle according to claim 1, wherein the electric actuator control section reduces an upper limit for the output torque of the electric actuator during the output restriction control.
 10. The working vehicle according to claim 1, further comprising a traveling body; and a revolving body swingably supported by the traveling body, the electric actuator being an electric motor which revolves the revolving body.
 11. A working vehicle control method comprising: determining a retention amount of a reducing agent inside a reducing agent tank; performing an output restriction control in which a signal which reduces an output of an engine is output when the retention amount is equal to or less than a first threshold; outputting a signal for restricting an output of an electric actuator during execution of the output restriction control; calculating an output of a power generator which is necessary for driving the electric actuator; determining an absorption torque of a hydraulic pump based on the output of the engine which is reduced and the restricted output of the power generator which is necessary for driving the electric actuator which is restricted; and outputting a command signal which indicates the absorption torque of the hydraulic pump which is determined.
 12. A working vehicle control method comprising: determining a retention amount of a reducing agent inside a reducing agent tank; performing an output restriction control in which a signal which reduces an output of an engine is output when the retention amount is equal to or less than a first threshold: outputting a signal for restricting an output of an electric actuator during execution of the output restriction control; calculating an output of a power generator which is necessary for driving the electric actuator; determining an absorption torque of a hydraulic pump based on the output of the engine which is reduced and the output of the power generator which is necessary for driving the electric actuator; and outputting a command signal which indicates the absorption torque of the hydraulic pump which is determined; outputting a stop command to the electric actuator when the retention amount is equal to or less than a second threshold which is smaller than the first threshold; and outputting a stop signal for an electric power control apparatus for the power generator and the electric actuator when an operation speed of the electric actuator is reduced to a predetermined speed and a torque command value to the power generator is zero after outputting the stop command.
 13. (canceled) 